diff --git a/lib/mergeset/block_header.go b/lib/mergeset/block_header.go
index ce4c8dd51..a957427ae 100644
--- a/lib/mergeset/block_header.go
+++ b/lib/mergeset/block_header.go
@@ -167,7 +167,7 @@ func unmarshalBlockHeadersNoCopy(dst []blockHeader, src []byte, blockHeadersCoun
 	for i := 0; i < blockHeadersCount; i++ {
 		tail, err := dst[dstLen+i].UnmarshalNoCopy(src)
 		if err != nil {
-			return dst, fmt.Errorf("cannot unmarshal block header: %w", err)
+			return dst, fmt.Errorf("cannot unmarshal block header #%d out of %d: %w", i, blockHeadersCount, err)
 		}
 		src = tail
 	}
diff --git a/lib/mergeset/block_stream_reader.go b/lib/mergeset/block_stream_reader.go
index 7e21cf44c..528a89017 100644
--- a/lib/mergeset/block_stream_reader.go
+++ b/lib/mergeset/block_stream_reader.go
@@ -297,8 +297,9 @@ func (bsr *blockStreamReader) readNextBHS() error {
 	// Unmarshal the unpacked index block into bsr.bhs.
 	bsr.bhs, err = unmarshalBlockHeadersNoCopy(bsr.bhs[:0], bsr.unpackedBuf, int(mr.blockHeadersCount))
 	if err != nil {
-		return fmt.Errorf("cannot unmarshal blockHeader #%d in the index block #%d: %w", len(bsr.bhs), bsr.mrIdx, err)
+		return fmt.Errorf("cannot unmarshal blockHeaders in the index block #%d: %w", bsr.mrIdx, err)
 	}
+	bsr.bhIdx = 0
 	return nil
 }